Summary
Little is known about the involvement of alpha-carotene in cardiovascular disease and cancer. This study evaluated the correlation between the concentration of alpha-carotene in blood serum and the risk of premature death in 15,318 Americans who were more than 20 years old. It was found that the risk of death from cardiovascular disease, cancer and all other causes reduced as the alpha-carotene levels in the blood increased. Therefore, eating fruits and vegetables high in alpha-carotene is recommended for the prevention of risk of an early death.

Introduction
Most chronic diseases like cancer and heart disease result in oxidative stress in the body, damaging DNA, proteins, and fats. The intake of antioxidants delays this process of oxidative damage. The human body acquires antioxidants from plant products like fruits and vegetables that are rich in carotenoids (alpha-carotene, beta-carotene, and so on). It has been reported that higher consumption of fruits and vegetables reduces the chances of cancer, heart disease, diabetes, and so on. Several reports have also shown that beta-carotene is not involved in the reduction of the risk of such diseases. Hence, it is apparent that alpha-carotene is responsible for the beneficial effects of carotenoids. This study attempts to find the link between serum alpha-carotene levels and an overall risk of death using long-term data on American adults.

Methods
* From 1988 to 1994, 15,318 participants aged 20 years or older were interviewed and followed up for 13.9 years. The data on age, race, education, health habits (smoking, drinking, and exercise) and body mass index (BMI) were recorded.
* Their serum beta and alpha-carotene levels were recorded using three different laboratory techniques. The total, high-density, and low-density cholesterol and blood pressure values were also recorded.
* A list of 113 causes of death was created based on internationally approved classification methods. The causes of death of the participants who had died were classified into three types: “cancer,” “heart disease (cardiovascular disease),” and “other.” These were further classified into subgroups.
* The subgroups were analyzed for alpha-carotene levels and their association with risk of death was statistically examined.

Results
* The average serum alpha-carotene level was 4.79 micrograms/dL. It was 4.22 micrograms/dL in men and 5.31 micrograms/dL in women.
* Upon analyzing data from 3,810 participants who had died by 2006, it was found that the serum alpha-carotene concentrations and risk of death from cancer, heart disease and all other causes were inversely related.
* Serum alpha-carotene concentrations were dependant on demography, lifestyle and health habits.
* Although alpha-carotene is chemically similar to beta-carotene, study results suggest that alpha-carotene, such as found in carrots, is about 10 times more effective than beta-carotene in inhibiting the proliferation of human cancer cells.

Shortcomings/Next steps
While high concentrations of alpha-carotene are beneficial, the inverse association between concentration and death-risk blurs beyond a certain value. Studies are needed to determine the optimum levels of alpha-carotene in blood. The classification of the causes of death may have become ambiguous because of diabetes, thereby affecting results. Moreover, several biomarkers for death or health habits may have been missed.

Conclusions
Increased concentrations of alpha-carotene in the blood reduce the threat of death by cancer, heart disease, and other similar diseases. Conversely, low alpha-carotene concentrations are associated with higher death risk due to these diseases. Alpha-carotene is known to be 10 times more successful than beta-carotene in stopping the spread of the cancer. Vegetables like carrots, sweet potatoes, spinach, and green beans are high in alpha-carotene, and their consumption is associated with reduced risk of cancers. Owing to the obvious benefits of high levels of alpha-carotene in blood, consumption of two to four servings of fruit and three to five servings of vegetables every day is recommended.